17732174 Nasa Fastener Design Manual

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NASA'ReferencePublication1228March 1990

. _-

Fastener Design Manual

Richard T. Barrett. , :. ? .

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NASAReferencePublication12281990

National AeronautK;sandSpace AdministrationOffice of ManagementScientific and TechnicalInformation Division

Fastener Design Manual

Richard T. BarrettLewis Research CenterCleveland, Ohio


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Contents

PageSummary ............................................................................................................ 1Introduction ......................................................................................................... 1General Design InformationFastener Materials ..............................................................................................Platings and Coatings ..........................................................................................Thread Lubricants ...............................................................................................Corrosion .........................................................................................................Locking Methods ................................................................................................Washers ...........................................................................................................Inserts .............................................................................................................Threads ............................................................................................................Fatigue-Resistant Bolts .........................................................................................Fastener Torque ..................................................................................................Design Criteria

11

4569

10121315

................................................................................................... 17

Rivets and LockboltsRivets ............................................................................................................... 26Lockbolts .......................................................................................................... 30General Guidelines for Selecting Rivets and Lockbolts .................................................. 34

References ........................................................................................................... 35Appendixes

A--Bolthead Marking and Design Data ..................................................................... 36B--Bolt Ultimate Shear and Tensile Strengths ............................................................. 90C--Blind Rivet Requirements .................................................................................. 94

PAGE BLANK NOT FILMEDiii


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SummaryThis manual was written for design engineers to enable them

to choose appropriate fasteners for their designs. Subject matterincludes fastener material selection, platings, lubricants,corrosion, locking methods, washers, inserts, thread types andclasses, fatigue loading, and fastener torque. A section ondesign criteria covers the derivation of torque formulas, loadson a fastener group, combining simultaneous shear and tensionloads, pullout load for tapped holes, grip length, head styles,and fastener strengths. The second half of this manual presentsgeneral guidelines and selection criteria for rivets andlockbolts.

IntroductionTo the casual observer the selection of bolts, nuts, and rivets

for a design should be a simple task. In reality it is a difficulttask, requiring careful consideration of temperature, corrosion,vibration, fatigue, initial preload, and many other factors.

The intent of this manual is to present enough data on boltand rivet materials, finishes, torques, and thread lubricantsto enable a designer to make a sensible selection for a particulardesign. Locknuts, washers, locking methods, inserts, rivets,and tapped holes are also covered.

General Design InformationFastener MaterialsBolts can be made from many materials, but most bolts are

made of carbon steel, alloy steel, or stainless steel. Stainlesssteels include both iron- and nickel-based chromium alloys.Titanium and aluminum bolts have limited usage, primarilyin the aerospace industry.Carbon steel is the cheapest and most common bolt material.

Most hardware stores sell carbon steel bolts, which are usuallyzinc plated to resist corrosion. The typical ultimate strengthof this bolt material is 55 ksi.

An alloy steel is a high-strength carbon steel that can be heattreated up to 300 ksi. However, it is not corrosion resistantand must therefore have some type of coating to protect it from

corrosion. Aerospace alloy steel fasteners are usually cadmiumplated for corrosion protection.

Bolts of stainless steel (CRES) are available in a variety ofalloys with ultimate strengths from 70 to 220 ksi. The majoradvantage of using CRES is that it normally requires noprotective coating and has a wider service temperature rangethan plain carbon or alloy steels.

A partial listing of bolt materials is given in table I. Thefollowing precautions are to be noted:

(1) The bolt plating material is usually the limiting factoron maximum service temperature.

(2) Carbon steel and alloy steel are unsatisfactory (becomebrittle) at temperatures below -65 *F.

(3) Hydrogen embrittlement is a problem with mostcommon methods of plating, unless special procedures areused. (This subject is covered more fully in the corrosionsection.)

(4) Series 400 CRES contains only 12 percent chromium andthus will corrode in some environments.(5) The contact of dissimilar materials can create galvanic

corrosion, which can become a major problem. (Galvaniccorrosion is covered in a subsequent section of this manual.)

Platings and CoatingsMost plating processes are electrolytic and generate hydro-

gen. Thus, most plating processes require baking after platingat a temperature well below the decomposition temperatureof the plating material to prevent hydrogen embrittlement.However, heating the plating to its decomposition temperaturecan generate free hydrogen again. Thus, exceeding the safeoperating temperature of the plating can cause prematurefastener failure due to hydrogen embrittlement as well as lossof corrosion protection. (A summary of platings and coatingsis given in table II.)

Cadmium PlatingThe most common aerospace fastener plating material is

cadmium. Plating is done by electrodeposition and is easy toaccomplish. However, cadmium-plated parts must be bakedat 375 *F for 23 hours, within 2 hours after plating, to preventhydrogen embrittlement. Since cadmium melts at 600 *F, itsuseful service temperature limit is 450 *F.


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ORIGINAL PAGE ISOF POOR-QUALITY

Material

Carbon steelAllo y steels

A-2 86 s tainl es s

17--4PHstainless

17-7PHstainless

300 seri esstainless

410, 416, and430 stainless

U-212 stainl ess

lnconei 718stainless

lnconel X-750stainless

Waspalloystainless

Titanium

TABLE I.--SUMMARY OF FASTENER MATERIALS

Surfacetreatment

Zinc plateCadmium pl at e,

n ickel p la te ,zinc plate, orchromium platePassivated per

MIL-S-5002None

Passivated

Furnace oxidized

Passivated

Cleaned andpassivated perMIL-S-5002Passivated perQQ-P-35 orcadmium platedNone

None

None

Useful designtemperature

limit,*F

-65 to 250-65 to

limitingtemperatureof plat ing

-423 to 1200

-300 to 600

-200 to 600

-423 to 800

-250 to 1200

1200

-423 to 900or cadmiumplate l imit- 320 to 1200

-423 to 1600

-350 to 500

Ultimate tensilestrength at room

temperature,ksi

55 and upUp to 300

Up to 220

Up to 220

Up to 220

70 to 140

Up to 180

185

Up to 220

Up to 180

150

Up to 160

Comments

Some can beused at 900 *F

Oxidat ion reducesgalling

47 ksi at 1200 *F;will corrodeslightly

140 ksi at 1200 *F

136 ksi at 1200 *F

Zinc PlatingZinc is also a common type of plating. The hot-dip method

of zinc plating is known commercially as galvanizing. Zinccan also be electrodeposited. Because z inc plating has a dullfinish, it is less pleasing in appearance than cadmium.However, zinc is a sacrificial material. It will migrate touncoated areas that have had their plating scratched off, thuscontinuing to provide corrosion resistance. Zinc may also beapplied cold as a zinc-rich paint. Zinc melts at 785 *F but hasa useful service temperature limit of 250 *F. (Its corrosion-inhibiting qualities degrade above 140 *F.)Phosphate Coatings

Steel or i ron is phosphate coated by treating the materialsurface with a diluted solution of phosphoric acid, usually bysubmerging the part in a proprietary bath. The chemicalreaction forms a mildly protective layer of crystallinephosphate. The three principal types of phosphate coatings are

zinc, iron, and manganese. Phosphate-coated parts can bereadily painted, or they can be dipped in oil or wax to improvetheir corrosion resistance. Fasteners are usually phosphatedwith either zinc or manganese. Hydrogen embrittlementseldom is present in phosphated parts. Phosphate coatings startdeteriorating at 225 *F (for heavy zinc) to 400 *F (for ironphosphate).

Nickel PlatingNickel plating, with or without a copper strike (thin plating),is one of the oldest methods of preventing corrosion and

improving the appearance of steel and brass. Nickel platingwill tarnish unless it is followed by chromium plating. Nickelplating is a more expensive process than cadmium or zincplating and also must be baked the same as cadmium afterplating to prevent hydrogen embrittlement. Nickel plating isgood to an operating temperature of 1100 *F, but is still notfrequently used for plating fasteners because of its cost.


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TABLE II.--SUMMARY OF PLATINGS AND COATINGS

Type of coating

Cadmium

Zinc

Phosphates:ManganeseZincIron

! Chromium

I .SliverBlack o xide(and oil)

Preoxidation(CRES) fastenersonly

Nickel

SermaGard andSermatel W

Stalgard

Dif fused nickel -cadmium

Useful des igntemperature limit,

*F

45O

140 to 250

225225 to 375

400

800 to 1200

1600a300

1200

1100

450 to 1000

475

900

Remarks

Most common for aerospacefasteners

Self-h eali ng and cheap erthan cadmium

M ildl y corrosi on res ist antbut main use is for surfacetreatment prior to painting.Another use is with oil orwax for deterring corrosion.

Too expensive for mostapplications other thandecorative

Most expensive coatingIne ffect ive in cor rosionprevention

Prevents freeze-up of CRESthreads due to oxidationafter installation

More expensive than cadmiumor zinc

Di spers ed aluminum part icleswith chromates in a water-based ceramic base coat

Proprietary organic and/ororganic -inorganic compoundused for corrosion resistanceand lubrication (in some cases

Expensive and requires closecontrol to avoid hydrogendamage

aoil boiling point

Ion-Vapor-Deposited Aluminum PlatingIon-vapor-deposited aluminum plating was developed by

McDonnell-Douglas for coating aircraft parts. It has someadvantages over cadmium plating:

(1) It creates no hydrogen embrittlement.(2) It insulates against galvanic corrosion of dissimilar

materials.(3) The coating is acceptable up to 925 *F.(4) It can also be used for coating titanium and aluminums.(5) No toxic byproducts are formed by the process.

It also has some disadvantages:(1) Because the process must be done in a specially designed

vacuum chamber, it is quite expensive.(2) Cadmium will outperform ion-vapor-deposited aluminum

in a salt-spray test.

Chromium PlatingChromium plating is commonly used for automotive and

appliance decorative applications, but it is not common forfasteners. Chromium-plated fasteners cost approximately asmuch as stainless steel fasteners. Good chromium platingrequires both copper and nickel plating prior to chromiumplating. Chromium plating also has hydrogen embrittlementproblems. However, it is acceptable for maximum operatingtemperatures of 800 to 1200 *F.

Sermatel W and SermaGardSermatel W and SermaGard are proprietary coatings I

consisting of aluminum particles in an inorganic binder withchromates added to inhibit corrosion. The coating material iscovered by AMS3126A, and the procedure for applying it byAMS2506. The coating is sprayed or dipped on the part andcured at 650 *F. (sPs Technologies: has tested Sermatel W-coated fasteners at 900 F without degradation.) This coatingprocess prevents both hydrogen embrittlement and stresscorrosion, since the fastener is completely coated. Sermatelis about as effective as cadmium plating in resisting corrosionbut costs about 15 percent more than cadmium. Fasteners arenot presently available "off the shelf" with Sermatel W orSermaGard coating, but the company will do small orders forfasteners or mechanical parts. These coatings will take up to15 disassemblies in a threaded area without serious coatingdegradation.

StalgardStalgard is a proprietary coating 3 process consisting of

organic coatings, inorganic-organic coatings, or both forcorrosion resistance. According to Stalgard test data theircoatings are superior to either cadmium or zinc plating in salt-spray and weathering tests. Stalgard coatings also providegalvanic corrosion protection. However, the maximumoperating temperature of these organic coatings is 475 F.

Diffused Nickel-Cadmium PlatingThis process was developed by the aerospace companies for

a higher temperature cadmium coating. A 0.0004-in.-thicknickel coating is plated on the substrate, followed by a0.0002-in.-thick. cadmium plate (per AMS2416). The part isthen baked for 1 hour at 645 *F. The resulting coating canwithstand 1000 *F. However, the nickel plate must completelycover the part at all times to avoid cadmium damage to thepart. This process is expensive and requires close control.

tSermatech International, Inc., Li merick, Pennsyl vania.2Jenkintown, Pennsylvania.3EIco Industries, Rockford, Illinois.


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Silver PlatingSilver plating is cost prohibitive for most fastener applica-

tions. The big exception is in the aerospace industry, wheresilver-plated nuts are used on stainless steel bolts. The silverserves both as a corrosion deterrent and a dry lubricant. Silverplating can be used to 1600 *F, and thus it is a good high-temperature lubricant. Since silver tarnishes from normalatmospheric exposure, the silver-plated nuts are commonlycoated with clear wax to prevent tarnishing. Wax is a goodroom-temperature lubricant. Therefore, the normal "drytorque" values of the torque tables should be reduced by50 percent to allow for this lubricant.

Passivation and PreoxidationStainless steel fasteners will create galvanic corrosion or

oxidation in a joint unless they are passivated or preoxidizedprior to assembly (ref. 1). Passivation is the formation of aprotective oxide coating on the steel by treating it briefly withan acid. The oxide coating is almost inert. Preoxidization isthe formation of an oxide coating by exposing the fastenersto approximately 1300 *F temperature in an air furnace. Thesurface formed is inert enough to prevent galling due togalvanic corrosion.

Black Oxide CoatingBlack oxide coating, combined with an oil fi lm, does little

more than enhance the appearance of carbon steel fasteners.The oil film is the only part of the coating that preventscorrosion.

Thread LubricantsAlthough there are many thread lubricants from which to

choose, only a few common ones are covered here. The mostcommon are oil, grease or wax, graphite, and molybdenumdisulfide. There are also several proprietary lubricants suchas Never-Seez and Synergist ic Coatings. Some thread-lockingcompounds such as l_x_tite can also be used as lubricants fora bolted assembly, particularly the compounds that allow thebolts to be removed. A summary of thread lubricants is givenin table III.

Oil and GreaseAlthough oil and grease are the most common types of thread

lubricants, they are limited to an operating temperature notmuch greater than 250 *F. (Above this temperature the oilor grease will melt or boil off.) In addition, oil cannot be usedin a vacuum environment. However, oil and grease are goodfor both lubrication and corrosion prevention as long as theseprecautions are observed.

TABLE III.--SUMMARY OF THREAD LUBRICAN TS

T ype of lub ri cant

Oil or grease

GraphiteMolybdenum

Useful des igntemperature

limit,*F

250

a212 to 250750

Remarks

Most common; cannot be used invacuum

Cannot be used in vacuumCan be used in vacuum

disulfideSynergistic

CoatingsNeverseez

Si lver Go op

Thread-lockingcompounds

500

2200

1500

275

Can be used in vacuum

Because oi l boi ls off, must beapplied after each high-temperature application

Do not use on aluminum ormagnesium part s; ext remel yexpensive

"Removable fastener" compoundsonly

aCarrierboiloff temperature.

Graphite"Dry" graphite is really not dry. It is fine carbon powder

that needs moisture (usually oil or water) to become alubricant. Therefore, its maximum operating temperature islimited to the boiling point of the oil or water. It also cannotbe used in a vacuum environment without losing its moisture.Because dry graphite is an abrasive, its use is detrimental tothe bolted joint if the preceding limitations are exceeded.

Molybdenum DisulfideMolybdenum disulfide is one of the most popular drylubricants. It can be used in a vacuum environment but

turns to molybdenum trisulfide at approximately 750 *F.Molybdenum trisulfide is an abrasive rather than a lubricant.Synergistic CoatingsThese proprietary coatings 4 are a type of fluorocarbon

injected and baked into a porous metal-matrix coating to giveboth corrosion prevention and lubrication. However, themaximum operating temperature given in their sales literatureis 500 *F. Synergistic Coatings will also operate in a vacuumenvironment.NeverseezThis proprietary compound 5 is a petroleum-base lubricant

and anticorrodent that is satisfactory as a one-time lubricant4General Magnaplate Corporation, Ventura, California.5Bostic Emhart, Broadview, lllinois.


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Analternative is to use a high-strength carbon steel (suchas H- 11 tool steel with an ultimate tensile strength of 300 ksi)and provide corrosion protection. However, it is preferableto use more fasteners of the ordinary variety and strength, ifpossible, than to use a few high-strength fasteners. High-strength fasteners (greater than 180 ksi) bring on problemssuch as brittleness, critical flaws, forged heads, cold rollingof threads, and the necessity for stringent quality controlprocedures. Quality control procedures such as x-ray, dyepenetrant, magnetic particle, thread radius, and head radiusinspections are commonly used for high-strength fasteners.Hydrogen Embrittlement

Hydrogen embrittlement occurs whenever there is freehydrogen in close association with the metal. Since mostplating processes are the electrolytic bath type, free hydrogenis present. There are three types of hydrogen-metal problems:

(1) Hydrogen chemical reaction: Hydrogen reacts with thecarbon in steel to form methane gas, which can lead to crackdevelopment and strength reduction. Hydrogen can also reactwith alloying elements such as titanium, niobium, or tantalumto form hydrides. Because the hydrides are not as strong asthe parent alloy, they reduce the overall strength of the part.

(2) Internal hydrogen embrittlement: Hydrogen can remainin solution interstitially (between lattices in the grain structure)and can cause delayed failures after proof testing. There isno external indication that the hydrogen is present.

(3) Hydrogen environment embrittlement: This problem isonly present in a high-pressure hydrogen environment suchas a hydrogen storage tank. Unless a fastener was under stressinside such a pressure vessel, this condition would not bepresent.

Most plating specifications now state that a plated carbonsteel fastener "shall be baked for not less than 23 hours at375 -4- 25 *F within 2 hours after plating to provide hydrogenembrittlement relief" (per MIL-N-25027D). In the past theplating specifications required baking at 375 25 *F for only3 hours within 4 hours after plating. This treatment was foundto be inadequate, and most plating specifications were revisedin 1981-82 to reflect the longer baking time. Hydrogenembrittlement problems also increase as the fastener strengthincreases.Cadmium Embrittlement

Although hydrogen embrittlement failure of materials is welldocumented (ref. 3), the effects of cadmium embrittlement arenot. In general, hydrogen embrittlement failure of cadmium-plated parts can start as low as 325 *F, but cadmiumembrittlement can start around 400 *F. Since both elementsare normally present in elevated-temperature failure ofcadmium-plated parts, the combined effect of the two can bedisastrous. However, the individual effect of each isindeterminate.

Locking MethodsTapped Holes

In a tapped hole the locking technique is normally on thefastener. One notable exception is the Spiralock 7 tap shownin figure 1. The Spiralock thread form has a 30* wedge rampat its root. Under clamp load the crests of the male threadsare wedged tightly against the ramp. This makes lateralmovement, which causes loosening under vibration, nearlyimpossible. Independent tests by some of the aerospacecompanies have indicated that this type of thread is satisfactoryfor moderate resistance to vibration. The bolt can have astandard thread, since the tapped hole does all the locking.Locknuts

There are various types of locking elements, with thecommon principle being to bind (or wedge) the nut thread tothe bolt threads. Some of the more common iocknuts arecovered here.Split beam.--The split-beam locknut (fig. 2) has slots in the

top, and the thread diameter is undersized in the slottedportion. The nut spins freely until the bolt threads get to theslotted area. The split "beam" segments are deflected outwardby the bolt, and a friction load results from binding of themating threads.

Wedge ramps resisttransverse movement

Figure l.--Spiralock thread.

Full-height,heavy-duty hex

Figure 2.--Split-beam locknut.

7Distributedby Detroit Tap&Tool Company, Detroit, Michigan,throughlicense from H.D. Holmes.


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Figure 7.--Jam nut.

Figure 8.--Durlock nut.Serrated-face nut (or bolthead).--The serrated face of this

nut (shown in fig. 8) digs into the bearing surface during finaltightening. This means that it cannot be used with a washeror on surfaces where scratches or corrosion could be aproblem.

According to sPs Technologies, their serrated-face bolts(Durlock 180) require 110 percent of tightening torque toloosen them. Their tests on these bolts have shown them tohave excellent vibration resistance.Lockwiring.--Although lockwiring is a laborious method

of preventing bolt or nut rotation, it is still used in criticalapplications, particularly in the aerospace field. The nutsusually have drilled corners, and the bolts either havethroughholes in the head or drilled comers to thread thelockwire through. A typical bolthead lockwiring assembly isshown in figure 9(a), and a typical nut lockwiring assemblyis shown in figure 9(b).

(a)

(b)(a) Multiple fastener application(double-twist method, single hole).(b) Castellated nuts on undrilled studs (double-twist method).Figure 9.--Lockwiring.

Direct interfering thread.--A direct interfering thread hasan oversized root diameter that gives a slight interference fitbetween the mating threads. It is commonly used on threadedstuds for semipermanent installations, rather than on bolts andnuts, since the interference fit does damage the threads.Tapered thread.--The tapered thread is a variation of the

direct interfering thread, but the difference is that the minordiameter is tapered to interfere on the last three or four threadsof a nut or bolt as shown in figure 10.Nutplates.--A nutplate (fig. 11) is normally used as a blind

nut. They can be fixed or floating. In addition, they can have

Easystart Lockingactionstarts

Totalsealandlockingaction

Figure 10.--Tapered thread.


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(a) (b)(a) Fixed.(b) Floating.

Figure l l .- -Nutplate.

ost of the locking and sealing features of a regular nut.utplates are usually used on materials too thin to tap. Theye used primarily by the aerospace companies, since theirstallation is expensive. At least three drilled holes and twoets are required for each nutplate installation.cking AdhesivesMany manufacturers make locking adhesives (or epoxies)r locking threads. Most major manufacturers make severalades of locking adhesive, so that the frequency ofsassembly can be matched to the locking capability of theesive. For example, Loctite 242 is for removable fasteners,d Loctite 2719 is for tamperproof fasteners. Othernufacturers such as Bostik, NO Industries, Nylock, 3M, andrmaloc make similar products.Most of these adhesives work in one of two ways. They are

a single mixture that hardens when it becomes a thiner in the absence of air or an epoxy in two layers that doesharden until it is mixed and compressed between the mating

Note that the two-layer adhesives are usually put onfastener as a "ribbon" or ring by the manufacturer. Thesebons or rings do have some shelf life, as long as they aret inadvertently mixed or damaged.These adhesives are usually effective as thread sealers as

However, none of them will take high temperatures. Thest adhesives will function at 450 *F; the worst ones will

at only 200 *F.

Washers

Belleville washers (fig. 12) are conical washers used morer maintaining a uniform tension load on a bolt than forking. If they are not completely flattened out, they servea spring in the bolt joint. However, unless they have

rrations on their surfaces, they have no significant lockingpability. Of course, the serrations will damage the matingrfaces under them. These washers can be stacked in

Loctite Corporation, Newington, Connecticut.

combinations as shown in figure 13 to either increase the totalspring length (figs. 13(a) and (c)) or increase the springconstant (fig. 1303)).Lockwashers

The typical helical spring washer shown in figure 14 is madeof slightly trapezoidal wire formed into a helix of one coil sothat the free height is approximately twice the thickness of thewasher cross section. They are usually made of hardenedcarbon steel, but they are also available in aluminum, silicon,bronze, phosphor-bronze, stainless steel, and K-Monel.

The lockwasher serves as a spring while the bolt is beingtightened. However, the washer is normally flat by the timethe bolt is fully torqued. At this time it is equivalent to a solidflat washer, and its locking ability is nonexistent. In summary,a lockwasher of this type is useless for locking.

=(a)_ L

(a) Smooth.(b) Serrated.

F igure 12. --Types of Bel levi lle washer s.

--F.hl ii.d._t_


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(a)

(b)

\\ \\_\\\\\\\\\\\\ \\\x\(c}(a) In series.

0a) In parallel,(c) In-p arallel series.

Figure 13.--Combinations of Bellevi lle washers.

Figure 14.--Helical spring washers.

Tooth (or Star) LockwashersTooth lockwashers (fig. 15) are used with screws and nuts

for some spring action but mostly for locking action. The teethare formed in a twisted configuration with sharp edges. Oneedge bites into the bolthead (or nut) while the other edge bitesinto the mating surface. Although this washer does providesome locking action, it damages the mating surfaces. Thesescratches can cause crack formation in highly stressedfasteners, in mating parts, or both, as well as increasedcorrosion susceptibility.Self-Aligning WashersA self-aligning washer is used with a mating nut that has

conical faces as shown in figure 16. Because there is both aweight penalty and a severe cost penalty for using this nut,it should be used only as a last resort. Maintaining parallelmating surfaces within acceptable limits (2" per SAEHandbook(ref. 4)) is normally the better alternative.

(a) (b)(a) Fiat.(b) Countersunk.

Figure |5.--Tooth lockwashers.

8" maximum mlsallgnment of nut andbearing surface at assemblyFigure 16.--Self-aligning nut.

InsertsAn insert is a special type of device that is threaded on its

inside diameter and locked with threads or protrusions on itsoutside diameter in a drilled, molded, or tapped hole. It is usedto provide a strong, wear-resistant tapped hole in a soft materialsuch as plastic and nonferrous materials, as well as to repairstripped threads in a tapped hole.

The aerospace industry uses inserts in tapped holes in softmaterials in order to utilize small high-strength fasteners tosave weight. The bigger external thread of the insert (nominally1/8 in. bigger in diameter than the internal thread) gives, forexample, a 10-32 bolt in an equivalent 5/16-18 nut.

In general, there are two types of inserts: those that arethreaded externally, and those that are locked by some methodother than threads (knurls, serrations, grooves, or interferencefit). Within the threaded inserts there are three types: the wirethread, the self-tapping, and the solid bushing.Threaded InsertsWire thread.--The wire thread type of insert (Heli-coil J0)

10Emhart Fastening Systems Group, Heli-Coil Division, Danbury,Connecticut.

10


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(a) Slotted,Co)Nylok.

Figure 19.--Self-tappinginserts.

Figure 17.--Wire thread insert installation. locking combinations, such as the Nyiok plug (fig. 19(b)) orthe thread-forming Speedser I deformed thread (fig. 20). Anadditional advantage of the thread-forming insert is that itgenerates no cutting chips, since it does not cut the threads.However, it can only be used in softer materials.

I1_ Deformed

(a) (b)(a) Free running.

Co)Locking.Figure 18.--Wire thread insert types.

is a precision coil of diamond-shaped c_s wire that formsboth external and internal threads as shown in figure 17. Thecoil is made slightly oversize so that it will have an interferencefit in the tapped hole. In addition, this insert is available witha deformed coil (fig. 18) for additional locking. The tang isbroken off at the notch after installation.

The wire thread insert is the most popular type for repairof a tapped hole with stripped threads, since it requires theleast amount of hole enlargement. However, the solid bushinginsert is preferred if space permits.Self-tapping.--Most of the self-tapping inserts are the solidbushing type made with a tapered external thread similar to

a self-tapping screw (fig. 19). There are several different

I

IFigure20.--Speedsert.

HRexnord Specialty Fasteners Division. Torrance,California.

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Solid bushing.--Solid hushing inserts have conventionalthreads both internally and externally. A popular type is theKeensert I1 shown in figure 21. The locking keys are drivenin after the insert is in place. Another manufacturer uses atwo-prong ring for locking. These inserts are also availablewith distorted external thread or Nylok plugs for locking.Nonthreaded InsertsPlastic expandable.--Tbe most familiar of the nonthreaded

inserts is the plastic expandable type shown in figure 22. Thisinsert has barbs on the outside and longitudinal slits that allowit to expand outward as the threaded fastener is installed,pushing the barbs into the wall of the drilled hole. (See ref. 5.)Molded in place.--This type of insert (fig. 23) is knurled

or serrated to resist both pullout and rotation. It is commonlyused with ceramics, rubber, and plastics, since it can develophigher resistance to both pullout and rotation in these materialsthan self-tapping or conventionally threaded inserts. (Seeref. 5.)Ultrasonic.--Ultrasonic inserts (fig. 24) have grooves in

various directions to give them locking strength. They areinstalled in a prepared hole by pushing them in while they arebeing ultrasonically vibrated. The ultrasonic vibration meltsthe wall of the hole locally so that the insert grooves are"welded" in place. Since the area melted is small, these insertsdo not have the holding power of those that are molded inplace. Ultrasonic inserts are limited to use in thermoplastics.(See ref. 50

Figure 21.--Keensert.

Figure 22. --P|a st ic expandable insert.

Figure 23.--Molded-in-place insert.

Figure 24.--Ultrasoni c ins erts .

ThreadsTypes of ThreadsSince complete information on most threads can be found

in the ANSl standards (ref. 6), the SAEHandbook (ref. 4), andthe National Institute of Standards and Technology (formerlythe National Bureau of Standards) Handbook H-28 (ref. 7)no thread standards will be included in this handbook. Thegoal here is to explain the common thread types, along withtheir advantages and disadvantages. The common thread typesare unified national coarse (UNC), unified national fine (UNF),unified national extra fine (UNEF), ONJC, UNJF, UNR, UNK,and constant-pitch threads.Unified national coarse.--UN is the most commonly used

threadon general-purpose fasteners. Coarse threads are deeperthan finethreadsand areeasierto assemblewithoutcrossthreading. The manufacturing tolerances can be larger thanfor finer threads, allowing for higher plating tolerances, uNcthreads are normally easier to remove when corroded, owingto their sloppy fit. However, a UNC fastener can be procuredwith a class 3 (tighter) fi t i f needed (classes to be covered later).

Unified national fine.--UNF thread has a larger minordiameter than UNC thread, which gives UNF fasteners slightlyhigher load-carrying and better torque-locking capabilities thanUN fasteners of the same identical mater ial and outsidediameter. The fine threads have tighter manufacturingtolerances than UNC threads, and the smaller lead angle allowsfor finer tension adjustment. UNF threads are the most widelyused threads in the aerospace industry.Unified national extra fine.--UNEF is a still finer type of

thread than UNF and is common to the aerospace field. Thisthread is particular ly advantageous for tapped holes in hardmaterials and for thin threaded walls, as well as for tappedholes in thin materials.

12


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UNJC and UNJF threads.--"J" threads are made in bothternal and internal forms. The external thread has a much

root radius than the corresponding UNC, UNR, UNK, orthreads. This radius is mandatory and its inspection isquired, whereas no root radius is required on UNC, UNF,UNEF threads. Since the larger root radius increases thenor diameter, a UNJF or UNJC fastener has a larger net tensileea than a corresponding UNF or UNC fastener. This rootadius also gives a smaller stress concentration factor in thereaded section. Therefore, high-strength (> 180 ksi) bolts

have "J" threads.UNR threads.--The UNR external thread is a rolled UN

in all respects except that the root radius must beounded. However, the root radius and the minor diameter

not checked or toleranced. There is no internal UNR thread.UNK threads.--The UNKexternal threads are similar to UNRreads, except that the root radius and the minor diametertoleranced and inspected. There is no internal UNK thread.

According to a survey of manufacturers conducted by thedustrial Fasteners Institute, nearly all manufacturers ofternally threaded fasteners make uNa rolled threads rathern plain uN. The only exception is for ground or cut threads.Constant-pitch threads.--These threads offer a selection of

that can be matched with various diameters to fit aarticular design. This is a common practice for bolts of 1-in.ameter and above, with the pitches of 8, 12, or 16 threadser inch being the most common.A graphical and tabular explanation of UN, UNR, UNK, andthreads is given on page M-6 of reference 8. A copy25) is enclosed here for reference.

lasses of ThreadsThread classes are distinguished from each other by themounts of tolerance and allowance. The designations run fromA to 3A and 1B to 3B for external and internal threads,espectively. A class 1 is a looser fitting, general-purposeread; a class 3 is the closer-toleranced aerospace standardread. (The individual tolerances and sizes for the variouslasses are given in the SAE Handbook (ref 4).)orming of ThreadsThreads may be cut, hot rolled, or cold rolled. The mostommon manufacturing method is to cold form both the headnd the threads for bolts up to 1 in. in diameter. For boltsbove 1-in. diameter and high-strength smaller bolts, the heads

hot forged. The threads are still cold rolled until the boltize prohibits the mater ial displacement necessary to form thehreads (up to a constant pitch of eight threads per inch).hreads are cut only at assembly with taps and dies or by latheCold rolling has the additional advantage of increasing thetrength of the bolt threads through the high compressiveurface stresses, similar to the effects of shot peening. Thisrocess makes the threads more resistant to fatigue cracking.

Fatigue-Resistant BoltsIf a bolt is cycled in tension, it will normally break near

the end of the threaded portion because this is the area ofmaximum stress concentration. In order to lessen the stressconcentration factor, the bolt shank can be machined downto the root diameter of the threads. Then it will survive tensilecyclic loading much longer than a standard bolt with the shankdiameter equal to the thread outside diameter.Fatigue (Cyclic) Loading of BoltsThe bolted joint in figure 26 (from ref. 9) is preloaded with

an initial load F,, which equals the clamping load Fc, beforethe external load Fe is applied. The equation (from ref. 11)for this assembly is

where Fb is the total bolt load. In this equation Kb is thespring constant of the bolt and K,. is the spring constant of theclamped faces. To see the effects of the relative springconstants, let R = Kc/Kb. Then (from ref. 10)

fh = F/+ Fe

In a normal clamped joint Kc is much larger than Kb(R = 5.0 for steel bolt and flanges), so that the bolt load doesnot increase much as the initial external load Fe is applied.(Note that the bolt load does not increase significantly untilFe exceeds Fi.)

In order to further clarify the effect of externally appliedloads, a series of triangular diagrams (fig. 27, from ref. 11)can be used to illustrate loading conditions.

Triangle OAB is identical in all four diagrams. The slopeof OA represents the bolt stiffness; the slope of AB representsthe joint stiffness (joint is stiffer than bolt by ratio OC/CB.)In figure 27(a) the externally applied load Fe(a) does notload the bolt to its yield point. In figure 27(b) the bolt is loadedby Fe(b) to its yield point, with the corresponding decreasein clamping load to FcL. In figure 27(c) external load Fe(c)has caused the bolt to take a permanent elongation such thatthe clamping force will be less than Fi when F_(c) isremoved. In figure 27(d) the joint has completely separatedon its way to bolt failure.

Note that the flatter the slope of OA (or the larger the ratioOC/OB becomes), the smaller the effect Fe has on bolt load.Therefore, using more smaller-diameter fasteners rather thana few large-diameter fasteners will give a more fatigue-resistantjoint.

Referring to figure 27(a), note that the cyclic (alternating)load is that portion above F i. This is the alternating load

13


20/104

ORIGINAL PAGE ISOF POOR QUALITY

T1_is I_ilga ie not m scr_v qdllreld eluIndlnd. _ould n0t be uied ii i working _eet. ind d_)4dld only radar l_e rlecl-er tlo I_e pincer ANSI StindanM do,leant wha_n Iita full Ihteld details on working dlul IH'a c_lLlined.

60" SCREW THREAD NOMINAL FORMS (SEE ANSI STANDARDS FOR FURTHER DETAILS)

TL

N 1 _zo_o F

?_

114READIDENTIFICATION

ANSI ISTANDARDSDOCUMENT5

UN THREADSInternal and External

Un,tied Screw Threads_ll-t960 ,See PageM--7I Met_icTranslahon8110-1968

Gages and Gaging forUn,|*ed Screw Threadsfi l 2-1966

UNR THREADS

_rno) Only

Und,ed Scre_ Th reads_1 .)-19b0 See PageM--T) Metr,c T rans la ti anBI .)o--1968 ,Drab)UNR Addendum tOB1.1-1960 rSee PageM--I9_

Gages an d Gaging _orUn*fied Scr*- Threadsfit .2-1966

External lhread RootE_ERNAL may be Flat ae E_ternai Thread RootROOT Rounded Radius Requ,r ed

EXTERNAL External Thread M,nor External Thread MmnorMINOR O,ameter is not D,ameter mSnot

DIAMETER _'o_ er anted ToSeronced

E3TERNAL UN Classes IA 2A UNR Classes I A. 2ATHREADS and 3A and 3A

UN Classes lB. 2Bo_d 38

INTERNALTHREADS

ANGLE ANDLEAD

TOLERANCE

Ino,v,dually Eq_,valent_oSO_olPD [olerance

Checked only whenSpat,had

Na InfernO| ThreadsDes,gnated UNR

UNR Motes _,th UNI nr ef na i Thr ead

I nd, vl du al ly Eau, vai entso 50% of P D l'ole_ance

Checked only _henSpeohed

Uh, l( 11'1READS

[:ti er na[ Only

,Oro(ll B$ ._ 4 ta_ Farmand Conformance

Ex ter nal Thr ead RootRadku s Mandator VCheck Reclu*r ed

Ex ter nal Thr ead M,norDiameter ,sio)e,anced

UNK Cl asses 2Aand 3A

No Interna l ThreadsDes,gnated UNK

Mates _ifh UN or UNJI nt erna l Thr ead

Ind_v,dually Equ,vaient Ito 40_ of P D ToleranceMandatory CheckRequ,red

UNJ THREADS

Internal and External

'Dratt_BI ?Sfa, Fo,mand Caniormanle NaRadius Rec;u,red onInternal Thread,

External Thread RootRadius Mondo_oryCheck Requ, r ed

E=lerna; Thread MinorI O,ameter ,SToleranced

UNJ Class 3A MatesOnly _,th UHJ In_e_nolThreads

UNJ Classes 3E and3EG No Rod,usRequ,red on InternalThread"

Indiv,duatly Equ,valentIO 40% of PO Toteronce

Mandatory CheckRequ,r ed

NOTI_S: 1 Refe tO i _e aogtoor$ aNe _(an_3(_s. As hst'gd 10 COrnplele thread Oela,is and conformance _atJ The a_proD;late current StanOar_ ,_ ' J' _e authoh ta tl _e docunl en_

tot con_oie(e cletatlsover ln,s s_eet

2 T_ese Star.lards may

and dSta. an_ _akes oreledepce

be oDta'neO Inrouqn AS,'_AE

Figure 25.--Explanation of uN, UNR, UNK, and uNs threads. (From ref. 8.) Reprinted with permission of Industrial Fasteners Institute.

14


21/104

__._....._v___..._.._ro(al

Fb -- F I

(b)(a) Bolted flanges with external load.(b) Free body with no external load.

(c) Free body with external load.Figure 26.--Fatigue loading of bolts.

v

(c)

_o Fr0m

Fj

Ultimate bolt load line

F Bolt preload line _Yield bolt load line

! A .

0 C B 0 C B 0 C B 0 CElongation

Z. Joint(a) (b) (c) (d) separation

Figure 27.--Bolt external loading.

(stress) to be used on a stress-versus-load-cycles diagram ofthe bolt material to predict the fatigue life of the bolts. Notethat an initial preload Fi near the bolt yields minimizes cyclicloading.Thermal Cyclic Loading of BoltsIf the bolt and joint are of different materials, an operating

temperature higher or lower than the installation temperaturecan cause problems. Differential contraction can cause the jointto unload (or separate); differential expansion can causeoverloading of the fasteners. In these cases it is commonpractice to use conical washers (see washer section of thismanual) to give additional adjustments in fastener and jointloading.

Fastener TorqueDetermining the proper torque for a fastener is the biggest

problem in fastener installation. Some of the many variablescausing problems are

(1) The coefficient of friction between mating threads(2) The coefficient of friction between the bolthead (or nut)and its mating surface(3) The effect of bolt coatings and lubricants on the frictioncoefficients(4) The percentage of bolt tensile strength to be used for

preload(5) Once agreement is reached on item 4, how to accuratelydetermine this value(6) Relative spring rates of the structure and the bolts

15


22/104

IGINAL PAGE ISPOOR QUALITY

A

ZI--

Z5m,JZI[

O

23


30/104


NATIONAL AEROSPACE S'."/_,iMDARDAEROSPACE INOU_TRIE_ ASSOCIATION OF AME'_I_._ IN: _?_,,i DE _ALIr. G_"_, L_ T K' _R' "dlt A l lIH I IqG ? (_ ID ZOO2f

-, .)'

;,X.JP_

Lh

wOC

"l t_Z

Z_L

_-_:i-_ ] .'

, : - -,!-:

HI'

OZz >o

_o_

v_z

YOT

CODE: BASIC PART NUMBER DESIGNATES. _OMINA.L DL_METEK.DASH NUMBER DESIGNATF$ GRIP A_P. LF3,:G'IH _SEE SHEET 3':.A_I)_ "A" TO DASH NUMBER FOP. UNDR!L: ED B9". TADD "H'" TO DASH NUMBER =OR DRILLED M_,,,.D 9NP _.NO CODE LETTER DESIGNATES DRILLED SPANK ONLY.

EXAMPLE NASI003-_ =. 1900 DIAMErEP. BOLT..500 GRIP, DRILLED SHANK ONLY.NASI003-8A = .1900DIAMETER BOI.T..SGOCRIP, UNDRILLED.NASIOO3- 8H = 19OO I.)IAME'i'EI_ bOLT..$0_: GRIP, DRILLED HEAD ONLY.

/._/// /j_//// // , /MATERIAL: CRES. A-286 SPEC AMS573$ OR AMS5?3";' ,O_,,,IDW.2*,_(_Y/S, II_,J_W._ _JyE XCEP'T ULTIMATE k,_,)

TENSILE STRFNGTH 140,_00 P SI M IN IM VM *,T BOOM TEMPERATURE, FABRICATED TO AMS74:8.

FINISH" CLEAN AND PASSIVATE !N ACCORDANCF ':, ,'Tlt.._'/.'_.5_ / (_-)-P-?,_ C" )NOTI'S | REFERENCE D!MLNSIONS ARE FOR D[.SIGN PURPOSES ONLY AND NO1 AN INSPI'CTION REQG',REMEN'T.

4.(a, _.

G ,,-I I.

,d; 8,

2. MAGNETIC PERMEABILITY SHALL BE LESS THAP 2.0 (AIR = 1.o, FOR A FIELD STRENCTH H 200, OERSTIEDS(MAGNETIC PERMEABILITY INDICATOR .."_...'_ ;,l_, -I -!?214 OR EOUi'_AL; N_T.)BOLTS SHALL BE I REE FP.O_E BUI_RS A];D SL_'LRE.TH_:S_ BOLTS ARE IN1"EN._,!!D ,:GF, !.'f_ :.._ 1! ';:2; R _-.T'JI(LS IJp 10 12C_ FGRIP!,[:NGIH FROM !JNL'r._ SIDEGF HL.,_IJ rO _.:':i _0", lULL CYLINDRICALPOR';'ION OF StI_NK.C_TTI:F, ;'!N HOLE C; NTI!RLINI _:!TP.IN 01'; ANL) NORMA;. WFTIIIN ._OF BOLT ( 'E lCTERL INE."l-J" DIA MAXIMUM NOT TO EXCE;; "'B": V.I! :I_,,UB,: DL.', _.l l OP OF HEAD NO'; LESS THAN "'H".C'(3NCF,_TRICIT'V: "H'" AN:_ "'A" DIAMT'.TEEJ ",V,T!;:X' ' ",1" VALUES TIP, "_" AND THREAD PITCH DIAMETERV,", rlltN "'_" VALUES TIFL

_el ,) SIIANK STRAIGH'F,_Q'SS. WIB'II|N "Z'" V_LL'|,_; TIF, P_I'. INC._: OF L_NGT tl(_110. BEARING SURFACE SQU,_.ENESS; WITh)IP < .G '.!. , TiP, WITH SHANK.

! I , DI ML 'Y S/ ONS IN IN('llLSIOLl R._.NCES L'NLF.SS OTHFI:._J.ISI" SP_.'r :_I" ', ..k';{;L_ S .'._:

_j DIS( ._,LO_ I_;ACTIVk I OL ! _[ S: (; " -_. t- I' [F JUt ', ! . I ', "( >

PC-,

_P

cZ

>

t

24

41-_7 Ru_ A_Wlllhm_lln D C _014

Figure 32.--Continued.

!

I NAS 13 THRU 12SHZLeT 2.a

IRe 111_J



31/104

RIGINAL PAGE ISF POOR QUALITY

NATIONAL AEROSPACE STANDARDAcPlOSPAC [ |NOUSTAIES ASSOCIATION OF" AMERICA. INC . t725 lie SALES STREET N W WAIHINGTON D C ZOO3G

I 0

K

I.I.ILI

_ASX NO. IIII_IC.A.T[S GRIP LENGTH ZN 0625 INCREMEhTS INTF.KHEDIATE OR LONGER L.,F..NGTHS MAY BE O[13EKED Iiy USE OF PROPER DASH NO.G

_,_ iw_ d_trd_l_ by Nml*on|l $umol_cP. _ao(_lT, o_ inc44137 R_D A_Wum_lto_ D C 20014

Figure 32.--Concluded.

I NAS 1003 THRU 1020SHEET 3AlrOl l_ lC . I i _u lf r, i- . A I. Io (* ll bO .n 0 f Ami ,, t. l _t_ 1979A_t r ,_ lts r lsm lo

ORJG._HAL PAGE ISOF POOR QUAL!TY

6Z0u_

o,

:ElidI.-,(r.

o.(

25


32/104

.am L

Pan Binding

Filllster

Truss Plain(carriage)

Figure 33.--Bolthead and screwhead styles.

Washer Hex

Alsoundercut,trim, and100 heads.Hex washer

Rivets and LockboltsRivets

Rivets are relatively low-cost, permanently installedfasteners that are lighter weight than bolts. As a result, theyare the most widely used fasteners in the aircraft manufacturingindustry. They are faster to install than bolts and nuts, sincethey adapt well to automatic, high-speed installation tools.However, rivets should not be used in thick materials or intensile applications, as their tensile strengths are quite lowrelative to their shear strengths. The longer the total grip length(the total thickness of sheets being joined), the more difficultit becomes to lock the rivet.

Riveted joints are neither airtight nor watertight unlessspecial seals or coatings are used. Since rivets are permanentlyinstalled, they have to be removed by drilling them out, alaborious task.

General Rivet TypesThe general types of rivets are solid, blind, tubular, and

metal piercing (including split rivets). From a structural designaspect the most important rivets are the solid and blind rivets.Solid rivets.--Most solid rivets are made of aluminum so

that the shop head can be cold formed by bucking it with apneumatic hammer. Thus, solid rivets must have cold-formingcapability without cracking. A representative listing of solidrivets is given in table IX (ref. 21). Some other solid rivetmaterials are brass, SAE 1006 to SAE 1035, 1108 and 1109steels, A286 stainless steel, and titanium.

Note that the rivets in table IX are covered by militarystandard specifications, which are readily available. Althoughmost of the solid rivets listed in table IX have universal heads,there are other common head types, as shown in figure 34.However, because the "experts" do not necessarily agree onthe names, other names have been added to the figure. Notealso that the countersunk head angle can vary from 60* to 120"although 82* and 100" are the common angles.

TABLE IX.--ALUMINUM AND OTHER RIVET MATERIALS

[From ref. 21.]

Material Rivet Rivet heads Applicationsdesignation available

2117-T4

2024-T4

1100

5056-H32

! Monel(annealed)

Copper(annealed)7050-T73

AD

DD

A

B

M

Universal (MS20470)100" Flush (MS20426)Universal (MS20470)100" Fl ush (MS2042 6)

Unive rsal (MS20470)100' Flush (MS20426)Universal (MS20470)10 0" Flus h (M S2 0426)Univer sa l (MS20615)10 0" Flus h (M S2 0427)

100" Flush (MS20427)

Universal (MS20470)10 0" Flus h (MS20426)

General use formost applications

Use only as analternative to7050-T73 wherehighe r s tr engthis required

Nonstructural

Joints containingmagnesium

[Join ing s ta in le sssteels, titanium,and Inconel

Nonstructural

Use only wherehigher strengthis required

The sharp edge of the countersunk head is also removed insome cases, as in the Briles n3 BRFZ "fast" rivet (fig. 35), toincrease the shear and fatigue strength while still maintaininga flush fit.

Blind rivets.--Blind rivets get their name from the fact thatthey can be completely installed from one side. They have thefollowing significant advantages over solid rivets:

(1) Only one operator is required for installation.(2) The installation tool is portable (comparable to an

electric drill in size).

n3 Bril es Ri vet Corpo rati on, Ocean side. California.

26


33/104

Button

UTruss Flat Countersunk(brazier) (flush)

Figure 34.- -Uni ted States standard rivet heads.

UPan

(universal)

f Shear-bearing area

Shear-bearing area-Figure 35.--BRFZ "fast' rivet,

(3) They can be used where only one side of the workpieceis accessible.

(4) A given-length rivet can be used for a range of materialthicknesses.

(5) Installation time is faster than with solid rivets.(6) Clamping force is more uniform than with solid rivets.(7) Less training is required for the operator.

Blind rivets are classified according to the methods used toinstall them:

(1) Pull mandrel(2) Threaded stem(3) Drive pin

Specific types (brands) of blind rivets are covered insubsequent sections of this manual.

Pull-mandrel rivets: This rivet is installed with a tool thatapplies force to the rivet head while pulling a prenotchedserrated mandrel through to expand the far side of the tubularrivet. When the proper load is reached, the mandrel breaksat the notch. A generic pull-mandrel rivet is shown infigure 36.

Threaded-stem rivets: The threaded-stem rivet (fig. 37(a))has a threaded internal mandrel (stem) with the external portionmachined flat on two sides for the tool to grip and rotate. Thehead is normally hexagonal to prevent rotation of the tubularbody while the mandrel in being torqued and broken off.

Drive-pin rivets: This rivet has a drive pin that spreads thefar side of the rivet to form a head, as shown in figure 38.Although drive-pin rivets can be installed quickly, they are

DQrOU /

Rivet inserted

Start setting

Figure 36.--Pul l-mandrel rivet . (From ref . 5.)

usually not used in aerospace applications. They are usedprimarily for commercial sheet metal applications.

Tubular rivets.--Tubular rivets are partially hollow andcome in a variety of configurations. The generic form has amanufactured head on one side and a hollow end that sticksthrough the pieces being joined. The hollow end is cold formedto a field head.

Since extensive cold forming is required on these rivets, theymust be extremely ductile and are consequently made of low-strength materials. They are normally used for commercialapplications rather than in the aerospace industry.

Some specific types of tubular rivets are(1) Compression(2) Semitubular(3) Full tubular

27


34/104

Inserted Installed

/_ Hexagonal head--_ p_._

Inserted Installed

(a) (b)(a)One-piecebody. (Fromref. 5.)(b) Two-piece body. (From ref. 22.)Figure 37.--Threaded-stemrivets.

Figure 38.--Drive-pin rivet. (From ref. 5.)

I _. I

Figure 39.--Compression tubular rivet. (From ref. 5.)

Compression tubular rivets: A compression tubular rivet(fig. 39) consists of two parts that have an interference fit whendriven together. These rivets are used commercially in softmaterials and where a good appearance is required on bothsides of the part.

Semitubular rivets: The semitubular rivet (fig. 40) has a holein the field end (hole depth to 1.12 of shank diameter) suchthat the rivet approaches a solid rivet when the field head isformed.

Full tubular rivets: The full tubular rivet (fig. 41) has adeeper hole than the semitubular rivet. It is a weaker rivet thanthe semitubular rivet, but it can pierce softer materials suchas plastic or fabric.

Metal-piercing rivets.--Metal piercing rivets (fig. 42) aresimilar to semitubular rivets, except that they have greatercolumn strength. Part of the sandwich material is not drilled,and the rivet pierces all the way or most of the way throughwhile mushrooming out to a locked position.

Figure 40.--Semitubular rivet. (From ref. 5.)

Figure 41.--Full tubular rivet. (From ref. 5.)

28


35/104


36/104

I I(a) Insert CherryMAx rivet into prepared hole. Place pulling head over rive t s tem and apply f irm, steady pressure to seat head. Actuate tool.(b) Stem pulls into rivet sleeve and forms large bulbed blind head; seats rivet head and clamps sheets tightly together. Shank expansion

begins.(c) "Safe-lock" locking collar moves into rivet sleeve recess. Formation of blind head is completed. Shear-ring has sheared from

cone, thereby accommodating a minimum of _6 in. in structure thickness variation.(d) Driving anvil forms "safe-lock" collar into head recess, locking stem and sleeve securely together. Continued pulling fractures

stem, providing flush, burr-free, inspectable installation.Figure 45.--Cherry rivet installation.

TABLE X.--CHERRY RIVET MATERIALSMaterials

Sleeve Stem

5055 Aluminum Alloy steel5056 Aluminum caEsMonel CRESInco 600 Inco X750

Ultimateshear strength,

psi50 00050 00055 00075 000

Maximumtemperature.

*F

2502509O0

1400

Pop rivets.--Pop rivets 16 are familiar to most of the publicfor home repairs. However, they are not recommended forcritical structural applications. The stem sometimes falls outof the sleeve after the rivet is installed, and the symmetry ofthe blind (formed) head leaves much to be desired. Althoughthe pop rivet shown in figure 47 is the most common type,USMmakes a closed-end rivet and three different head styles.

16USM Corporation, Pop Rivet Division, Shelton, Connecticut.

LockboltsIn general, a Iockbolt is a nonexpanding, high-strength

fastener that has either a swaged collar or a type of threadedcollar to lock it in place. It is installed in a standard drilledhole with a snug fit but normally not an interference fit. Aiockbolt is similar to an ordinary rivet in that the locking collaror nut is weak in tension loading and is difficult to removeonce installed.

Some of the lockbolts are similar to blind rivets and canbe completely installed from one side. Others are fed into theworkpiece with the manufactured head on the far side. Theinstallation is then completed from the near side with a gunsimilar to blind rivet guns. Lockbolts are available with eithercountersunk or protruding heads.Since it is difficult to determine whether a Iockbolt isinstalled properly, they should be used only where it is notpossible to install a bolt and nut of comparable strength.However, they are much faster to install than standard boltsand nuts.

30


37/104

Lock collar cap __ _

:_rat e_ _:_ _dc:: l : rpl i"type optional)

(a)

I_-Grip_,- 1

Sleeve

(b)(a) Protruding head, BP-T (MS90354) or BP-EU (MS21141).

(b) Ins ta lled fas tene r.Figure 46.--Huck blind rivets,

Figure 47.--Pop rivet installation.

Hi-LokThe Hi-Lok n7 lockbolt has a countersunk or protruding

manufactured head and threads like a bolt. It is fed throughthe hole from the far side. The installation gun prevents shankrotation with a hexagonal key while the nut is installed (asshown in fig. 49). The nut (collar) hexagonal end is notchedto break off at the desired torque. Hi-Lok lockbolts areavailable in high-strength carbon steel (to 156-ksi shear),stainless steel (to 132-ksi shear), and titanium (to 95-ksi shear).Huckbolts

Huckbolts t5 are similar to Hi-Loks except that the stem isusually serrated rather than threaded. The collar is swagedon the stem. Then the stem is broken at the notch as shownin figure 50. Huckboits and their collars are available in carbonsteel, aluminum, and stainless steel with various strengths, aslisted in the Huck catalog.

Jo-BoltsJo-boits are similar to blind rivets in appearance and

installation. The locking collar (sleeve) is expanded to forma shop head by rotating the threaded stem with a gun. Thethreaded stem is notched and breaks off when the proper torqueis reached. A typical Jo-bolt installation is shown in figure 48.

Taper-LokTaper-Lok t8 is a high-strength threaded fastener that is

17Hi-Shear Corporation, Torrance, California.nsSPS Technol ogies, Jenki ntown , Pen nsylv an ia.1.,+.1

Stem--/Vd//AX,..utTypical installation

J+Figure 48.--Jo-bolt. (From ref. 21.)

31


38/104

(a)

JJltltlUfltltltRIllllltlllllttlllllULj.---_;--___j

/-Remaining portion of

a.era.semb,.I device automatically, shears off

,.____+ _.(b)(a) Hi-Lok pin.

(b) Hi-Lok pin and collar after assembly.Fi gure 49 .--Hi -Lo k inst al latio n.

-_C__ i-PA_ Grip + D = Maximum lengthGrt

_'--_ Brazier head -I (Figure 50.--Installed Huckbolt fastener.length in 16ths

Fi gure 51. --Taper-Lo k inst allati on.

Forged head

Typical installation

installed with an interference fit. Most of the shank is taperedon a 1.19" angle. The lubricated Iockbolt is driven into adrilled and reamed hole. The interference fit allows the nut(tension or shear nut) to be installed and torqued to the requiredvalue without holding the Iockbolt to prevent rotation (seefig. 51). The nuts are iocknuts with captive washers. Whena tension nut is installed, this fastener can take as much tensionload as a bolt of the same size and material. Consequently,Taper-Loks are used in critical applications where cyclicloading is a problem. Taper-Lok Iockbolts are available inhigh-strength alloy steel, H-I 1 tool steel, and several stainlesssteels, as well as titanium.

RivnutsA Rivnut 19 is a tubular rivet with internal threads that is

deformed in place to become a blind nutplate (fig. 52). Rivnutsare available with protruding, countersunk, and fillister heads.They are also available with closed ends, sealed heads, ribbedshanks, hexagonal shanks, and ribbed heads. Since theunthreaded tubular portion of the rivet must deform, thematerial must be ductile. Consequently, the Rivnut materi,tlsare fairly low strength, as shown in table XI.

I';'B.F. Goodrich, Engineered Systems Di',ision. Akron. Ohio.

32


39/104


l ,1

(a) (b) (c) (d) (e)(a) Step 1--Rivnut fastener is threaded onto mandrel of installation tool.

(b) Step 2--Rivnut fastener, on tool mandrel, is inserted into hole drilled for installation.(c) Step 3--Mandrel retracts and pulls threaded portion of Rivnut fastener shank toward blind side of work, forming bulge in unthreaded

s hank area.(d) Step 4--Rivnut fast ener is cl inched securely in place; mandrel is unthreaded, leaving imernal Rivnut threads intact.

(e) Blind nutplate--Properly installed Rivnut fastener makes excellent blind nutplate for simple screw attachments; countersunk Rivnutfasteners can be used for smooth surface installation.

Figure 52. --Rivnut ins ta llat ion.

TABLE XI.--STANDARD RIVNUT FASTENERMATERIALS AND FINISHES

Material

Aluminum

Steel

Stainlesssteel

Brass

Type

6053-T4

C- 1108'C-1110 a

4037

430

305 aCarpenter 10 dAlloy 260

Standard fi nish

Anodize--Alumilite 205will meet specifications:MIL-A-8625 (ASG)

Cadmium plate--O.0002 in.minimum thickness perQQ-P-416b, class 3,type I

Cadmium plate--O.0002 in.minimum thickness perQQ-P--416b, class 2,type II

Pickled and passivated perQQ-P-35, type II

None--bright as machined

None--bright as machined

Minimumultimatetensile

strength,psi

28 000

45 000

b55 000c85 UO0

67 000

80 000

50 000ac-I IO8andC-I 110 steel may beused interchange.ably.bNo 4 andNo. 6 thread sizes.CNo.8--I12-mthreadize.d305 andCarpenterNo. 10 stainless steel may be used interchangeably.

Hi-Shear RivetHi-Shear 17 rivets consist of a high-strength carbon steel,

stainless steel, aluminum, or titanium rivet (pin) with a necked-down shop head, as shown in figure 53. The collar (2024aluminum or Monel) is swaged on to give a finished head that

t Pin_

Pin groove edgemust show

Collar-_Pin triiming edge

Figure 53. --Hi-Shea r ins tal la tion .

can be visually inspected for proper form. This rivet shouldbe used for shear applications only, as the collar has negligibletensile strength.

Although this rivet has been partially superseded by variouslockbolts, it is still being used in aircraft and aerospaceapplications.Lightweight Grooved Proportioned LockboitThe lightweight grooved proportioned lockbolt (LGPL) 2 is

made especially for composite materials. It has both anoversize head and an oversize collar to lessen contact stresses

20Monogram Aerospace Fasteners, Los An geles, Cali fo rn ia.

33


40/104

(al (b) (c) (d)(a) Flanged collar is placed over lightweight pin.(b) Installation tool grips and pulls pin, drawing sheets tightly together and removing sheet gap.(c) As pull on pin increases, tool anvil swages flanged collar into lockinggrooves and forms permanent vibration-resistant lock.

(d) Pull on pin continues until pin fracturesat breakneck groove and is then ejected. Tool anvil disengages swaged collar.Figure 54.--LGPLinstallation.

on the composite material during both installation and servicelife. The shank is high-strength (95-ksi shear) titanium andthe collar is 2024 aluminum. It is installed with a lockbolt toolas shown in figure 54.

General Guidelines for Selecting Rivetsand LockboitsA number of standard documents are available for the

selection, installation, and drawing callout of rivets andlockbolts as follows:(1) Rivet installations are covered by MIL-STD-403. This

specification covers pilot holes, deburring, countersinking,dimpling, and the application of zinc chromate paint betweendissimilar materials. Other specifications for corrosionprevention of drilled or countersunk surfaces are covered inMIL-P-116 and MIL-STD-171.

(2) Design and selection requirements for blind structuralrivets are given in MS33522 (appendix C).

(3) Design and selection requirements for blindnonstructural rivets are given in MS33557.

(4) A wealth of information on allowable rivet strengths invarious materials and thicknesses is given in chapter 8 ofMIL-HDBK-5 (ref. 18).(5) Testing of fasteners is covered by MIL-STD- 1312.

(6) Lockwiring is done per MS33540.Note that the nominal rivet spacing for a rivet pattern is an

edge distance of 2D and a linear spacing of 4D, where D isthe rivet diameter. However, the 4D spacing can be increasedif sealing between rivets or interrivet buckling is not a problem.

Solid rivets (expanded during installation) should not be usedin composite materials, as they can overstress the hole andcause delamination of the material.

Lewis Research CenterNational Aeronautics and Space AdministrationCleveland, Ohio, June 30, 1989

34


41/104


References1. Sliney, HE.: High Temperature Solid Lubricants--1. Layer Lat tice

Compounds and Graphite. Mech. Eng., vol, 96, no. 2, Feb. 1974,pp. 18-22 .

2. Prevention of Material Deterioration: Corrosion Control Course--U.S.Army Logistics Engineering Directorate--Nov. 1970.

3. ASM Metals Handbook. 9th ed., Vols. 1,2, 3, 5, 13, American Societyfor Metals, Metals Park. OH.4, SAE Handbook. SAE, 1968.

5. 1987 Fastening. Joining & Assembly Reference Issue. Mach. Des.,vol. 59, no. 27. Nov. 19, 1987.

6. Unified Inch Screw Threads (UN and UNR Thread Form). ANSIB 1.1-1982. American National Standards Institute, New York, NY,1982.

7. Screw Thread Standards for Federal Services, Part l--Unified UNJUnified Miniature Screw Threads. National Bureau of StandardsHandbook. NBS-H28-1969-PT- 1, 1969.

8. Fastener Standards. 5th ed., Industrial Fasteners Institute, Cleveland,OH, 1970.

9. Bickford, J.H.: An Introduction to the Design and Behavior of BoltedJoints. Dekker, 1981.

10. Juvinall, R.: Engineering Considerations of Stress. Strain. and Strength.McGraw-Hill, 1967.

11. Donald, E.P.: A Practical Guide to Bolt Analysis. Mach. Des., w)l. 53.Apr. 9, 1981, pp. 225-231.

12. Baumeister, et al.: Mark's Standard Handbook for Mechanical Engineers.8th ed., McGraw-Hill, 1978.

13. Seely, F.B.: Resistance of Materials. 3rd ed., Wiley & Sons, 1947.14. Shigley, J.E.; and Mitchell, L.D.: Mechanical Engineering Design. 4th

ed., McGraw-Hill, 1983.15. Machine Design, Nov. 19 , 19 81.16. Peery, D.J.: Aircraft Structures. McGraw'-Hill, 1950.t7. Grinter, L.: Theory of Modern Steel Structures. Vo[. I, Macmillan

Co., 1955.18. Metallic Materials and Elements for Aerospace Vehicle Structures.

MIL-HDBK-5E, Department of Defense, June 1987.19. Faupel, J.H.; and Fisher, F.E.: Engineering Design, 2nd ed., Wiley &

Sons, 1981.20. Fastener Technology International Magazine. Solon, Ohio, Oct. 1985

through Feb. 1987 Editions.21. Design Handbook, Section 16. McDonnell Douglas Astronautics Co..

Huntington Beach, CA.22. Bruhn, E.F. : Analysis & Design of Flight Vehicle Structures. Tri-State

Offset Co., Cincinnati, 1965.

35


42/104

Appendix ABolthead Marking and Design Data

[From ref. 20]

36


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Appendix BBolt Ultimate Shear and Tensile Strengths

[From ref. 18]

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Documents

17732174 Nasa Fastener Design Manual